VARIOUS METHODS OF HEATING DESCRIBED IN DETAIL. 223 



Suppose, then, that we have already solved the first part of 

 the problem, by attributing these results to the beneficial action 

 of gases arising from fermenting manure ; let us consider how 

 we can produce those gases, under other circumstances, i. ., with- 

 out the presence of manure. 



Ammonia is the result of a combination of the two gases, 

 hydrogen and nitrogen, and has been hitherto known to gar- 

 deners, and applied by them, chiefly in the state in which it 

 exists, and is produced by the decomposition of animal and veg- 

 etable matter, as in the formation of dung-beds, from which we 

 can perceive it escaping in an uncombined state into the atmos- 

 phere. It is easily distinguished from all other gases by its 

 powerful, penetrating odor. It remains, however, but a short 

 time in this state, as it is speedily absorbed by porous sub- 

 stances, and by living plants, and combines with other gases, 

 forming compounds ; with carbonic acid, for instance, forming 

 the carbonate of ammonia of the shops, from which it can read- 

 ily be disengaged and evolved into the atmosphere of a hot-house. 

 Ammonia, in the state of a carbonate, is exceedingly volatile, and 

 when a small portion is mixed with water, arid the temperature 

 raised to about 112 degrees, a large quantity of ammonia is 

 evolved. This will be still better effected by mixing a small 

 quantity of potash, soda, or lime, with the water in which the 

 ammonia has been absorbed. The salt which held the ammo- 

 nia in combination is taken up by these alkalies, and the ammo- 

 nia, being exceedingly volatile, escapes into the atmosphere. 



By dissolving the sulphate or carbonate of ammonia in hot- 

 water tanks, or in thin troughs placed over the pipes and flues, 

 an atmosphere may be produced strikingly similar to that of a 

 dung-bed, and capable of producing nearly similar effects. 

 Dung-beds are probably the most natural methods of applying 

 artificial heat to plants ; and it is yet doubtful if we shall ever 

 be able to supersede them in their invigorating influence, 

 although much may be done to modify the existing evils of arid 

 and unwholesome atmosphere in hot-houses. The mixture of 

 guano, pigeon's dung, and various other substances, gives off 

 large quantities of ammonia in warm water, and may be used 

 with advantage instead of its salts. Tanks afford an excellent 



